The combustors of gas turbine engines have a metal support shell that is protected from the heat of combustion gases by a ceramic lining made of multiple heat shields abutting together at their adjacent edges. The combustor shells and heat shields are perforated to permit compressed cooling air to pass from a surrounding plenum through the combustor shell into an intermediate cooling chamber then through the heat shield into the hot gases within the combustor. The heat shield and flow of cooling air prevent direct contact between the metal combustor shell and the hot combustion gases. The flow of cooling air cools the combustor shell and heat shields.
The compressed cooling air contained within the intermediate cooling chamber has a higher pressure than the combustion gases to propel the cooling air into the combustor in the intended direction of flow. Since the heat shields containing the compressed cooling air are made of multiple panels with edge joints and include openings for igniters and fuel nozzles, adequate sealing of the heat shield edges and openings is necessary to ensure that the flow of cooling air is controlled. Production of compressed cooling air in the air compressor of the engine consumes energy and accordingly excessive or uncontrolled leakage of cooling air represents a loss of energy and lower engine efficiency. For example, in some gas turbine engines, significant amount of cooling air is leaked through gaps between the heat shield and combustor wall. The leaked cooling air can be used more efficiently for cooling purposes if leakage volume is reduced and controlled.
It is desirable to reduce the uncontrolled leakage of cooling air around openings and edges of the heat shield panels within a combustor to reduce the unnecessary consumption of cooling air and thereby increase engine efficiency.